To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is underway based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation, and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
Currently, data traffic has increased dramatically due to the rapid spread of smartphones. The Korea Communications Commission (KCC) has reported that due to the accelerated spread of smartphones, mobile data traffic in 2013 was increased 3 times compared to the previous year. The number of smartphone users will further increase and application services using the smartphones will be more popularized, so the mobile data traffic is expected to increase much more than now. In particular, if even Machine-to-Machine Communication (MTM) utilizing things, such as communication between people and things and communication between things, which will provide a new mobile market, is commercialized in addition to the communication between people, the traffic that is transmitted to a Base Station (BS) or an evolved Node B (eNB) is expected to increase exponentially, so it may be difficult to deal with the traffic.
Therefore, technology capable of addressing these issues is needed, and currently, end-to-end direct communication technology has attracted much attention. This technology, called Device-to-Device (D2D) communication, has attracted attention in both the licensed band that is used by the cellular mobile communication, and the unlicensed band that is used by local communication, such as Wireless Local Area Network (WLAN).
If the end-to-end direct (or D2D) communication is integrated with the cellular mobile communication, it is noteworthy in that it is possible to increase the traffic capacity of the eNB and reduce the overload of the eNB. In other words, if terminals or multiple User Equipment (UEs) in the same cell or adjacent cells establish a D2D link between them, and then directly exchange data with each other though the D2D link without passing through the eNB, it is possible to advantageously reduce two links (e.g., a link from a UE to an eNB and a link from the eNB to another UE) to one link (e.g., a link from the UE to another UE).
Research in the unlicensed band is aimed to prevent the unnecessary waste of wireless resources by recognizing the needs for communication between people, communication between people and things, and communication between things, and to determine the locally generated traffic and properly service the traffic. Therefore, the research is focused on the method of efficiently operating the process in which a plurality of UEs broadcast information about the service or content to their surroundings and receive a response thereto.
In order to perform D2D communication, a process of setting up synchronization between UEs is needed. A UE may set up synchronization between UEs by using the time information received through a synchronous eNB or a Global Positioning System (GPS) reception module. In the scheme where a UE sets up synchronization between UEs by using the time information received through the synchronous eNB or the GPS reception module, the UE needs a connection to the synchronous eNB or the GPS reception module.
However, if the communication scheme provided by the communication operator does not support the synchronous eNB, the UE may not set up synchronization by using the time information received through the synchronous eNB. In addition, if a UE is located in a GPS shaded area (e.g., the space between skyscrapers, the tunnel, the interior of a building, and the like), the UE may not receive the time information from the GPS satellites, so the UE may not set up synchronization for D2D communication. As a result, if the UE's connection to the synchronous eNB or the GPS reception module is not smooth, the UE may not even initiate D2D communication.
Therefore, a need exists for a method and an apparatus for supporting synchronization for a D2D communication.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.